1. Field of the Invention
The present invention relates to a multiplex communication system, and in particular to a time division multiplex communication system for an automotive vehicle which can activate a plurality of loads (e.g. headlamps, power window motors, air conditioner, audio apparatus, etc.) by a plurality of switches, respectively via as small a number of transmission lines as possible.
2. Description of Prior Art
In a multiplex communication system for transmitting and receiving data between a master station and a plurality of slave stations via a single transmission line, various loads (lamps, motors, etc.) and switches are distributed in the slave stations, and these loads in the slave stations are activated respectively, whenever the corresponding switches in the slave stations are depressed. In the prior-art system, however, since the switch on-off conditions are read once for each access cycle for all the slave stations, in case a reading error occurs due to noise for instance, there exists a problem in that the load (motor, lamp, etc.) is activated erroneously on the basis of an erroneous data for one access cycle duration.
Further, in the case where the number of slave stations is large, it is preferable to classify the slave stations into a few groups according to power supply modes, that is, according to the ignition key switch positions (BAT, ACC and IGN modes) in the case of an automotive vehicle, in order to improve the response speed. Conventionally, however, since the loads are simply and mechanically allocated to the nearest possible slave stations, even if the slave stations including switches and loads to be activated only in the ACC and IGN modes are not accessed in the BAT mode, there still exists a problem in that many slave stations must be accessed in the BAT mode and therefore the response speed is low. In other words, it is preferable to change the switches and loads to be included in the respective slave stations according to the power supply mode, in order to minimize the response speed.
Further, in the conventional multiplex communication system, the format of the communication protocol is composed of one type of bit length (e.g. 16 bits), there exists a problem in that each item of communication data is long in bit length, so that the transmission efficiency is low; the cost is high; and soft error tends to occur in the IC chip because the communication speed becomes high.
The problems involved in the conventional multiplex communication system will be explained in further detail hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.